In the aviation field, the proper positioning of the center of gravity (CG) of an aircraft is essential. For example, if the CG of an aircraft is positioned too far forward of the aerodynamic center of the wing, a pilot can experience significant difficulty in attempting to control the aircraft during flight. Similarly, if the CG of the aircraft is positioned too far aft of the aerodynamic center of the wing, the aircraft will become inherently unstable.
Stated somewhat differently, in order to maintain proper stability of an aircraft, the CG should not under any condition of fuel loading, passenger loading, cargo loading, or any other type of loading be positioned rearward of a rear stability limit. And, in order to maintain proper control, for example, during take offs and landings, the CG should never be positioned forward of the aerodynamic limit of the aircraft.
One, thus, can readily understand that, when design criteria are altered for an aircraft, such as when a different passenger seating configuration is selected or a different propulsion system is selected, it can become necessary to shift, or reposition, the fuselage of an aircraft on its wing. And, where conventional aircraft manufacturing systems and techniques are employed, this can result in a complete redesign of the aircraft and the tools used to build or assemble it.
Those skilled in the art of aircraft manufacture and design will appreciate, therefore, that a need exists for an improved method of repositioning a fuselage on a wing, especially when significant design changes are encountered in an aircraft development process or desired to suit customer orders or requirements. The use of composite parts in aircraft has historically been limited, at least in part, due to the high financial entry barriers imposed by the cost of composite aircraft tooling or molds. The molds, also called tools, used to lay up and cure composite aircraft parts are expensive to manufacture and generally are usable to fabricate a limited number of parts before the mold must be replaced. One of skill in the art will recognize that it is desirable to limit the number of molds required to produce the necessary parts for an aircraft.
A related concern in the design of aircraft is that aircraft are comprised of a large number of parts. For composite aircraft, this would require the fabrication of many different molds to make even a portion of the parts. One of skill in the art will recognize that a reduction in the part count will reduce the number of molds required and simplify assembly and logistics, thereby reducing manufacturing costs. Composite parts generally are manufactured by laying up uncured composite material in a mold or tool, drawing a vacuum on the uncured material, curing the material in the mold at controlled conditions of temperature and humidity, and then removing the part from the mold.
Typically, any single part of a composite aircraft cannot have such a complex shape that the mold will close around itself to the extent that it blocks removal of the rigid composite part once it is cured. If the shape of a part is too complex, conventional composite manufacturing techniques require that it be produced as two or more separate parts that are bonded or otherwise fastened together. One of skill in the art will recognize that using multiple parts will increase the number of molds used, increase the production time, and thus increase the cost of manufacture.
Thus the composite aircraft designer is challenged by both the desire to reduce the parts count to reduce manufacturing and assembly costs and the need for flexibility to change features of parts while avoiding large retooling costs. If the designer can reduce the number of parts, the assembly and manufacture can be simplified and costs can be reduced. However, flexibility is necessary because design changes commonly occur and the molds or tools for at least some parts may need to be altered and certain optional design variations may be desirable to adapt an aircraft to suit customer preferences or operational requirements. One of skill in the art thus will recognize that a need exists for improved methods to manufacture complex composite parts for aircraft and to reduce both the part count for a composite aircraft and the number of molds or tools required to fabricate those parts.